The fluid catalytic cracking of hydrocarbons in modern refinery operations produces large amounts of C.sub.4 - fuel gas of little or no gasoline product value and the catalytic reforming of hydrocarbons produces large amounts of C.sub.6 aromatic hydrocarbon which though having value as gasoline blending stock is produced in excessive amounts.
The present invention particularly relates to a catalytic technique for upgrading light olefin gas to heavier hydrocarbons and to alkylating C.sub.6 to C.sub.8 aromatics to higher octane heavier lower alkyl aromatic hydrocarbons. It provides a continuous process for processing olefinic light gas feedstock, containing ethene and propene, or other lower alkenes, to produce C.sub.5 + hydrocarbons, such as olefinic liquid fuels, isobutane, aromatics, e.g. benzene, and other useful products and at the same time alkylating C.sub.6 to C.sub.8 aromatics to produce C.sub.1 to C.sub.4 lower alkyl substituted aromatic hydrocarbons for use as gasoline blending stock. Ethene (ethylene, C.sub.2 H.sub.4)-containing gases, such as petroleum cracking offgas, and catalytic reformate containing benzene, toluene, xylene and ethyl benzene are useful feedstocks for the process.
In particular, the present process provides a single product recovery system for two separate conversion reactions, a reforming reaction and an olefins oligomerization-alkylation reaction.
Developments in zeolite catalysis and hydrocarbon conversion processes have created interest in utilizing olefinic feedstocks for producing C.sub.5 + gasoline, diesel fuel, etc. In addition to basic chemical reactions promoted by ZSM-5 type zeolite catalysts, a number of discoveries have contributed to the development of new industrial processes. These are safe, environmentally acceptable processes for utilizing feedstocks that contain lower olefins, especially C.sub.2 -C.sub.4 alkenes and feedstocks containing aromatic compounds, especially C.sub.6 to C.sub.8 aromatics.
U.S. Pat. No. 3,729,409 (Chen) discloses improving the yield-octane number of a reformate by contacting the reformate in the presence of hydrogen over a zeolite catalyst. U.S. Pat. No. 4,150,062 (Garwood et al) discloses a process for the conversion of C.sub.2 to C.sub.4 olefins to produce gasoline which comprises contacting the olefins with water over a zeolite catalyst. U.S. Pat. No. 4,016,218 (Haag et al) and U.S. Pat. No. 3,751,506 (Burress) disclose processes for the alkylation of benzene with olefins over a ZSM-5 type catalyst. U.S. Pat. No. 4,209,383 (HeRoute et al) discloses the catalytic alkylation of benzene in reformate with C.sub.3 -C.sub.4 olefins to produce gasoline.
U.S. patent application Ser. No. 157,831, filed Feb. 19, 1988, relates to a process for preparing gasoline by contacting a C.sub.4 - fuel gas containing ethene and propene with a catalytic reformate containing C.sub.6 to C.sub.8 aromatic hydrocarbons over a zeolite catalyst. All of the above disclosures are incorporated herein by reference.
It has now been found that the amount of benzene in a gasoline product pool can be reduced by contacting a debutanized catalytic reformate feed with a fuel gas feed over a zeolite catalyst under olefins oligomerization and alkylation reaction conditions preferably in a fluidized bed reaction zone to obtain a product comprising alkylated aromatic hydrocarbons and oligomerized olefins, withdrawing the product from the fluidized bed reaction zone, and adding said product to a debutanizer column.
The C.sub.6 to C.sub.8 aromatics in the catalytic reformate can be converted to lower alkyl aromatic hydrocarbons while at the same time converting the C.sub.4 - olefins to C.sub.5 + hydrocarbons both of which products are suitable for use as gasoline blending stocks.